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Adaptive reward-related decision making often requires accurate and detailed representation of potential available rewards. Environmental reward-predictive stimuli can facilitate these representations, allowing one to infer which specific rewards might be available and choose accordingly. This process relies on encoded relationships between the cues and the sensory-specific details of the rewards they predict. Here, we interrogated the function of the basolateral amygdala (BLA) and its interaction with the lateral orbitofrontal cortex (lOFC) in the ability to learn such stimulus-outcome associations and use these memories to guide decision making. Using optical recording and inhibition approaches, Pavlovian cue-reward conditioning, and the outcome-selective Pavlovian-to-instrumental transfer (PIT) test in male rats, we found that the BLA is robustly activated at the time of stimulus-outcome learning and that this activity is necessary for sensory-specific stimulus-outcome memories to be encoded, so they can subsequently influence reward choices. Direct input from the lOFC was found to support the BLA in this function. Based on prior work, activity in BLA projections back to the lOFC was known to support the use of stimulus-outcome memories to influence decision making. By multiplexing optogenetic and chemogenetic inhibition we performed a serial circuit disconnection and found that the lOFC→BLA and BLA→lOFC pathways form a functional circuit regulating the encoding (lOFC→BLA) and subsequent use (BLA→lOFC) of the stimulus-dependent, sensory-specific reward memories that are critical for adaptive, appetitive decision making.

Predictive learning exerts a powerful influence over choice between instrumental actions. Nevertheless, how this learning is encoded in a sufficiently stable manner to influence choices that can occur much later in time is unclear. Here, we report that the basolateral amygdala (BLA) encodes predictive learning and establishes the memory necessary for future choices by driving the accumulation of delta-opioid receptors (DOPRs) on the somatic membrane of cholinergic interneurons in the nucleus accumbens shell (NAc-S). We found that the BLA controls DOPR accumulation via its influence on substance P release in the NAc-S, and that although DOPR accumulation is not necessary for predictive learning per se, it is necessary for the influence of this learning on later choice between actions. This study uncovers, therefore, a novel GPCR-based form of memory that is established by predictive learning and is necessary for such learning to guide the selection and execution of specific actions.

Contemporary theories emphasize the involvement of the endogenous opioid system in assigning hedonic values to rewards. Although earlier research supports this view, recent findings suggest that opioids play a larger and more complex role in reward processes than these theories suggest. For example, opioid activity in the basolateral amygdala is required for encoding incentive learning, a process by which the value of goal-directed actions is updated. Outside the amygdala, opioid receptors in the ventral striatum have been found to promote choice between different courses of action. Specifically, μ opioid receptors in the nucleus accumbens core and δ opioid receptors in the nucleus accumbens shell have been reported to mediate distinct aspects of incentive motivation; the core regulating the effect of experienced reward and the shell of predicted reward on choice. In both cases, the involvement of opioid receptors was restricted to the time of choice, although changes in their expression pattern could be observed prior to that point. This time-restricted involvement of opioid receptor-related processes is consistent with the view that opioids in the nucleus accumbens are central components of the limbic-motor interface, integrating reward-related information with instrumental learning to guide decision-making, particularly the selection and execution of goal-directed actions.This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.